Simplify slash reduction code.
Allow 'variables' in Nock expressions.
Now I can use the REPL to do symbolic manipulation, e.g.:
> eval "*[a 2 [1 1] c d]"
Fix infinite loop reducing /[2 a].
Remove some redundant calls to reduce.
Add a parser for Nock pseudocode.
Fully reduce nested formulas.
This is very incomplete, but usable. See the README for details.